Current aircraft air-ground data-link systems transport both air traffic control (ATC) data-link messages and non-ATC data-link messages on the same very high frequency (VHF) frequency. Both message types compete for the limited bandwidth available. Air traffic control (ATC) is a service provided by ground-based controllers, who direct aircraft on the ground and in the air. The primary purpose of ATC systems is to separate aircraft in order to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots. The non-ATC data-link messages are the messages other than traffic control messages.
Once a data-link message reaches the data link layer in the communication management unit, the transmission of the data-link message from the aircraft is strictly a first-in-first-out (FIFO) process. In currently available aircraft communication systems, the ATC data-link messages are sometimes delayed by non-ATC data-link messages being sent from the same aircraft despite the efforts to expedite the ATC messages. For example, a time-critical ATC data-link message can be delayed by a large non-ATC data-link message that was received at the data link layer prior to the ATC data-link message. If the delay is too long, the pilot and controller revert to using voice communication, which reduces the system efficiency and increases the workload for the pilot and controller.
Prior art solutions to overcome this delay of ATC data-link messages require adding another VHF radio and antenna to the aircraft and ground system, which is expensive.